1. Field of the Invention
The present invention relates to a rocking operation type electric component, such as a switch device, a variable resistor and the like, in which an operation knob is rocked (seesawed), and more particularly, to a mounting structure of the operation knob.
2. Description of the Related Art
Generally, a rocking operation type electric component, which serves, for example, as a switch device applied to a power window mechanism for a vehicle, includes an operation knob which can be rocked and has a bottomed case-shaped configuration, a signal generating unit which includes a movable element to be pressed and driven by the operation knob and generates a different electric signal in response to a position change of the movable element, and a case which receives the signal generating unit. The operation knob is rotatably mounted on a portion of the case.
FIG. 5 is an explanatory view illustrating an exemplary mounting structure of an operation knob in this kind of conventional electric component (for example, see Japanese Unexamined Patent Application Publication No. 9-259703 (page 2 and FIG. 6)). Referring to FIG. 5, in a bottomed case-shaped operation knob 50, a pair of rotation shafts 53 and 54 protrude outwards from left and right side walls 51 and 52, respectively. The operation knob 50 is inserted between a pair of wall portions 55 and 56 of a case which face each other. The wall portions 55 and 56 are provided with through-holes 55a and 56a, respectively. By outwardly fitting the rotation shafts 53 and 54 from the inside of the case into the through-holes 55a and 56a, respectively, the operation knob 50 is rotatably assembled with the case. At this time, a widthwise dimension of the operation knob 50 including the rotation shafts 53 and 54 is established to be slightly larger than a gap between the pair of wall portions 55 and 56 of the case. When assembling the operation knob 50 to the case, the operation knob 50 is inserted between the wall portions 55 and 56 with the side walls 51 and 52 elastically bent inward, and then, the rotation shafts 53 and 54 are snap-fitted into the corresponding through-holes 55a and 56a. By this fact, the operation knob 50 is rotatably supported by the wall portions 55 and 56 of the case. Therefore, by controlling the rotation of the operation knob 50 within a predetermined angle, the operation knob 50 can be rocked.
In another conventional exemplary construction, shafts are respectively formed on a pair of wall portions of a case which face each other, in such a way as to protrude outward. A pair of side walls of an operation knob are provided with installation holes into which the shafts can be fitted, respectively. The wall portions of the case are inserted between the pair of side walls of the operation knob, and the shafts of the case are respectively snap-fitted into the corresponding installation holes of the operation knob. By this fact, the operation knob is rotatably mounted on the wall portions of the case.
In the conventional rocking operation type electric component shown in FIG. 5, since the operation knob 50 is inserted to rock between the wall portions 55 and 56 of the case and the through-holes 55a and 56a into which the rotation shafts 53 and 54 are fitted are exposed to the outside, if liquid such as rain water or beverage adheres to the exposed surface of the operation knob 50 or the case, the liquid is likely to leak into the case through a gap between the wall portions 55 and 56 and the side walls 51 and 52 or a gap between the through-holes 55a and 56a and the rotation shafts 53 and 54. In this regard, because a signal generating unit including contact portions is arranged inside the case, if the liquid leaking into the case from the outside adheres to the signal generating unit, a short circuit or corrosion of the signal generating unit can be caused, and operational reliability of the rocking operation type electric component can be degraded. Further, because the rotation shafts 53 and 54 of the operation knob 50 are viewed from the outside, the design or the outer appearance of the rocking operation type electric component may be deteriorated.
Also, in the latter example, because the operation knob is installed to cover the pair of wall portions of the case which face each other, it is possible to accomplish a structure for preventing to some extent liquid such as rain water or beverage from leaking into the case. However, due to the fact that the installation holes of the operation knob into which the shafts of the case are snap-fitted are exposed to the outside, the possibility of liquid to leak into the case through the gap between the installation holes and the shafts still exists. Accordingly, leakage of liquid is not completely prevented. Also, because it is the norm that the operation knob has a strength which is no greater than that of the case, when adopting the structure in which the shafts of the case are snap-fitted into the installation holes of the operation knob, a mechanical strength is insufficient around the installation holes of the operation knob, and therefore, the operation knob is likely to be broken around the installation holes. Moreover, even in this conventional example, since the installation holes of the operation knob and the shafts of the case are viewed from the outside, the design or the outer appearance of the rocking operation type electric component is deteriorated.